System of distribution



Patented Mar. 8, 1927.

UNITED STATES PA ERNST F. W. ALEXANDERSON, F SCHENECTADY, NEW YORK,

ASSIGNOR TO GElVERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

.SYSTEM on DISTRIBUTION.

Application filed November 1, 1924. Serial No. 747,394.

My present invention relates to systems of electrical distribution, andmore particularly to systems for converting direct cur,- rent topolyphase alternating current.

One of the'objects of my invention is to provide a system of the classdescribed which will not require for its operation any device havingmoving parts. A further object of my invention is to provide an ap-.

paratus for the purpose mentioned, which will be especially adapted forhigh voltage direct current distribution systems.

- In carrying my invention into efi'ect, 1 provide a plurality of singlephase transformers, and supply current from the direct current source toeach primary winding through a pair of electric valves. In order thatthese valves should operate at the best efficiency they should becontrolled in such a way that current will flow only when the potentialdifference between the terminals is comparatively small andsubstantially the maximum current carried by the valve should bepermitted to flow therein duiing the entire period during'which the vale is rendered conductive. These valves may be of the pure electrondischarge type, or may be of the type which operate byreason of gasionization. In either case, the action of the,valve is controlled bymeans of a third electrode or grid of some convenient form.

In the-case of the valve operating by gas ionization, it is important inorder to secure good commutation of the current in trans fer-ringcurrent from one valve to another that the'current through one valveshould be reduced to zero at the time it is made non-conducting andcurrent starts in the other valve of each'pair. In the case of the valveoperatingby a pure electron discharge, this feature is not so important,but unless the current through each valve is reduced to a small amountat the time the valve is rendered non-conducting surges may be set upin. the system which will cause the insulation at some point to break bdown. In order to meet this requirement,

I provide means whereby the potential ap' plied to a valve is reversedat the instant that the valve is rendered non-conducting by theapplication of a negative potential to its grid. we

The novel features which I believe to be characteristic of my inventionare ,set forth with particularity'in the appended claims,

10 and 11.

my invention itself however, both as to its organization and method ofoperation will best be understood by reference to the followingdescription taken in connection with the accompanying drawmg m which Ihave shown diagrammatically a system for converting direct current tothree-phase alternating current.

have indicated in the drawing three pairs of valves, 1 and 2, 3 and 4, 5and 6, of the thermionic type for supplying current from direct currentmains 7 and 8, to the primary Windings9, 10 and 11, of threesingle-phase transformers 12, 13 and 14. The positive side 7 of thedirect current system is connected to the middle point of each primarywinding 9, 10 and 11, through inductive windings 15 to 20, inclusive.These windings may all be entirel independent of one another, butprefera ly will be wound upon a three legged closed magnetic core,windings 15 and being placed on one leg, windings 16 and 17 on thesecond leg, and windings Hand 19 on the third leg of the magnetic core.The windings are so connected that when equal currents are applied tothe three primary windings f, 10 and 11, the magnetomotive forces of thedifferent windings oppose each other, thus producing no flux in the coreupon which they are wound except for a slight leakage flux.

The secondary windings 21,22 and 23 are connected in delta to thethree-phase distribution mains 24, .25 and 26. Condensers 27, 28 and 29are connected across each phase of the distribution system throughtransformers 30, 31 and 32. These condensers may be connected directlyacross the secondaries of the transformers 12, 13 and 14 or acros theprimary windings 9, In case the valves operate by means of gasionization the latter connection is probablypreferable. The excitationfor the grids of the valves ,1 to 6 is obtained y means of transformers33, 34 and 35, which are connected to the distribution mains 24, and 26.The terminals of the secondaries of transformers 33, 34 and 35 areconnected to the grids-of the valves 1 to 6. through resistances 36..The mid points of the secondary windings are connected to the cathodesof valves 1 to 6 through resistances 37 and reactances 38. Currentforheating the cathodes of valves 1 to 6, which are all connected inparallel, may be sup plied by a source of direct current 39 or from anyother convenient source of current as desired.

In the operation of a system of the type described, it is necessary forsatisfactory operation that one valve of each pair should be madeconducting by the application of a positive potential to the grid beforecurrent has been interrupted in the other pair. This requires that thepositive voltages applied to the grids of the valves should lead thevoltages induced in the and 23. The desired lead in voltage may besecured by including condensers 40 in the circuit of the primarywindings of transtential is supplie formers 33, 34 and 35. In thearrangement shown, these condensers are connecte through transformers 41for the purpose of stepping down the current, and thus permitting theuse of a smaller condenser.

The use of phase control means for the purpose of causing the current tostart through one anode before itisinterrupted in the other is broadlyclaimed in a copending application of mine, Serial No. 651,409, filedJuly 13, 1923, and assigned to the same assignee as the presentapplication.

In the operation of the system described, I have found that although thecurrent wave flowing through each valve is ofsubstantial rectangularform, the potential set up in the secondary windings of the transformersis of substantially sine wave form.

" A substantially sine wave-potential is also primary windings 9, 10,

current is flowing throng one valve the potential upon the anode of theother valve is negative and of ahigh value, whereasthe potential set upacross the across the-valve which is conducting is com- The difier'encebetween the paratively low.

positive potential of the supply main 7 and the potential of the anodeof the valve which is conducting is taken up by the inductive windings15 to 20.

When the potential of the valve which is non-conducting has been reducedto zero or has become as current is permitted to flow through the valvethe condensers 27, 28 and 29., which have previously become charged,discharge, and as a result the potential across the valve which hadpreviously been carrying the current is momentarily reversed. Thiscauses a sudden interruption in the current through that valve and atthe same time'the potential of. the grid is made negative. I have foundtherefore that the system operates in.

windings 21, 22'

. supplying current supplying current positive, a positive poto itsgrid. As soon by Letters Patent of the United States, is:' 1.. Thecombination in a system'ofdistrtbution of a source of direct current, apolyphase system of transformers, having their secondaries connected toa polyphase distribution system, individual connections for supplyingcurrent from saidvsource to each of the primar windings of saidtransformers, an in uctive winding included in 'apair of electric eachof said connections, valves for controlling the fiow of current to eachof said primary windings, and means for controlling the action of saidvalves in such away that when current is permitted to start in one ofeach pair of said valves the potential applied to the other valve of thepair will be'momentarily reversed.

2. bution of a source of direct current, a polyphase system oftransformers, having their The combination in a system of distri-'secondaries connected to a polyphase distribution system, individualconnections for of the primawindings of said transformers, an in uctivewinding included in each of sai connections, all of said inductivewindin being wound upona common core, a pair of electric valves forcontrolling the flow of current to each of said primary windings, andmeans for controlling the action of said valves in such a way that whencurrent is permitted to start in one of each pair of said valves thepotential applied to the other valve of the pair will be momentarilyreversed;

3. The combination in a system of distribution of a source of directcurrent, a polyphase system of transformers having their secondariesconnected to a polyphase'distribution system, individual connections forfrom said source to each of the prima windings of said transformers, anin uctive winding included in each of said'connect1ons,-a pair ofelectric valves for controlling the flow of current from said source toeach' to eachof said primary windings, and .a

capacityassociated with each of said windings in such a way that whencurrent starts to flow through one of each pair of valves the potentialapplied to the other valve of the pair will be momentarily reversed bythe action of the capacity. In witness whereof, I my hand this 30th dayof October, 1924.

ERNST'F. W. ALEXANDERSON.

have hereunto set 4'

